Network providers have the need of testing mobiles under varying channel conditions. Only mobiles fulfilling certain constraints are delivered to customers. In order to avoid expensive real-world-measurements, these tests are performed in the laboratory. In order to simulate varying channel conditions, a channel simulator is used. The use of radio frequency faders is known. Such a radio frequency fader though is very expensive.
Alternatively, a baseband-simulator can be used. A radio frequency fader is advantageous since it is inserted into a path between the measurement and the device under test just as a transmission channel is in real-world measurement. A baseband-fader is advantageous since it is significantly less expensive and since the digital processing of the baseband-fader allows very easily reproducible measurement results. Typically though, baseband-faders can only be used on the downlink transmission channel, which corresponds to the transmission channel from the measurement device to the device under test. The uplink transmission channel, which corresponds to the transmission channel from the device under test to the measurement device, though is unchanged.
In most cases, this does not pose a problem since degrading the transmission channel from the device under test to the measurement device would only test the receiver of the measurement device, but not the device under test. Anyway, a demand exists for testing devices under test with activated uplink-fading. This is due to the need of the network providers to test the reaction of the device under test to the changed transmission conditions by adapting the modulation scheme, the coding scheme, the packet length, or the communication standard used by the device under test. Also a reaction of the device under test to data packets not received properly is a parameter in need of testing. Moreover, an overall data throughput under varying conditions is a parameter in need of testing.
The German patent application DE 101 24 371 A1 shows a measurement device comprising a baseband-fader as described earlier.
What is needed, therefore, is an approach for measuring the reaction of a device under test to changing uplink channel quality without requiring expensive hardware.